The Cenomanian - Turonian boundary oceanic anoxic event in East of Kopet-dagh basin (Amirabad section) with emphasis on calcareous nannofossils

In this study the succession comprising Aitamir and Abderaz Formation boundary is investigated along Amir Abad section in eastern Koppeh-Dagh region. Based on Calcareous nannofossils and NC biozonation scheme, Late Albian to Late Turonian time of deposition is estimated for the measured succession. There is some evidence such as paleoecological changes and increase in organic carbon burial, enabling recognition of the Cenomanian – Turonian Oceanic Anoxic Event (OAE2) in this section. Anoxic events often occur as a result of high productivity leading to increased burial of organic matter. Paleoecological trends recorded including decrease in abundance of Broinsonia spp. and Biscutum spp. and increase in Watznaueria spp. at the beginning of the late Cenomanian interval suggest prevalence of oligotrophic condition during this interval of time. In the late Late Cenomanian and Cenomanian-Turonian boundary intervals, the increase in relative abundance of surface water high fertility markers such as Biscutum spp. and the increase of fertility index i.e. (Biscutum旫ꂮ᚛皋)/Watznaueria, point to amore eutrophic condition. The absence of Nannoconus spp., which are not seen in anoxic conditions, is another evidence of OAE2. The rising trend of total organic carbon content in the Late Cenomanian part of the sedimentary succession and the mentioned paleoecological evidences, suggest presence of Late Cenomanian Oceanic Anoxic Event in eastern Koppeh-Dagh. Although this global event is mostly reported from oceanic black shales, in some sections especially in the east of Tethys, it is sometimes recorded in shallow water sediments. Shale and marl succession in Koppeh-Dagh region can be considered as the continuation of their global trend in the eastern-most part of the Tethyan realm where the Late Cenomanian Oceanic Anoxic Event (OAE2) has occurred in a rather shallow environment of deposition.